Asset Browser - Githubissues

Finally tackled this one. Closes #348. See below for open items, and the README for more details. This is how it currently looks:

TODO

[x] Remove whole selection, not just the clicked item
[x] Fix date
[x] When filtering through link, keep selected element selected.
[x] Handle asset preview loading when adding
[x] Add URLs and tags
[x] Simplify data structure (only store ref, no guid)
[x] Fix name not appearing in the grid
[x] Move a few more items from our tables into the lib
[x] Clean up previous code from @Vroonsh
[x] Merge the two query classes
[x] Add scrolling to details panel
[x] Make tag and attribute filter visibles in the details panel, and hitting them again should remove the query instead of adding a second one.
[ ] Re-organize the asset repository
[ ] Add proper documentation